DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Implementation

Mercurial (b66b287a2650)

VCS Links

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: sw=2 ts=8 et :
 */
/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Mozilla IPC.
 *
 * The Initial Developer of the Original Code is
 *   The Mozilla Foundation
 * Portions created by the Initial Developer are Copyright (C) 2009
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Chris Jones <jones.chris.g@gmail.com>
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */

#ifndef mozilla_ipc_Shmem_h
#define mozilla_ipc_Shmem_h

#include "base/basictypes.h"

#include "nscore.h"
#include "nsDebug.h"

#include "IPC/IPCMessageUtils.h"
#include "mozilla/ipc/SharedMemory.h"

/**
 * |Shmem| is one agent in the IPDL shared memory scheme.  The way it
    works is essentially
 *
 *  (1) C++ code calls, say, |parentActor->AllocShmem(size)|

 *  (2) IPDL-generated code creates a |mozilla::ipc::SharedMemory|
 *  wrapping the bare OS shmem primitives.  The code then adds the new
 *  SharedMemory to the set of shmem segments being managed by IPDL.
 *
 *  (3) IPDL-generated code "shares" the new SharedMemory to the child
 *  process, and then sends a special asynchronous IPC message to the
 *  child notifying it of the creation of the segment.  (What this
 *  means is OS specific.)
 *
 *  (4a) The child receives the special IPC message, and using the
 *  |mozilla::ipc::SharedMemoryHandle| (which is an fd or HANDLE) it
 *  was passed, creates a |mozilla::ipc::SharedMemory| in the child
 *  process.
 *
 *  (4b) After sending the "shmem-created" IPC message, IPDL-generated
 *  code in the parent returns a |mozilla::ipc::Shmem| back to the C++
 *  caller of |parentActor->AllocShmem()|.  The |Shmem| is a "weak
 *  reference" to the underlying |SharedMemory|, which is managed by
 *  IPDL-generated code.  C++ consumers of |Shmem| can't get at the
 *  underlying |SharedMemory|.
 *
 * If parent code wants to give access rights to the Shmem to the
 * child, it does so by sending its |Shmem| to the child, in an IPDL
 * message.  The parent's |Shmem| then "dies", i.e. becomes
 * inaccessible.  This process could be compared to passing a
 * "shmem-access baton" between parent and child.
 */

namespace mozilla {
namespace ipc {


class NS_FINAL_CLASS Shmem
{
  friend struct IPC::ParamTraits<mozilla::ipc::Shmem>;

public:
  typedef int32 id_t;
  // Low-level wrapper around platform shmem primitives.
  typedef mozilla::ipc::SharedMemory SharedMemory;
  typedef SharedMemory::SharedMemoryHandle SharedMemoryHandle;
  struct IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead {};

  Shmem() :
    mSegment(0),
    mData(0),
    mSize(0),
    mId(0)
  {
  }

  Shmem(const Shmem& aOther) :
    mSegment(aOther.mSegment),
    mData(aOther.mData),
    mSize(aOther.mSize),
    mId(aOther.mId)
  {
  }

#if !defined(DEBUG)
  Shmem(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
        SharedMemory* aSegment, id_t aId) :
    mSegment(aSegment),
    mData(aSegment->memory()),
    mSize(0),
    mId(aId)
  {
    mSize = *PtrToSize(mSegment);
  }
#else
  Shmem(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
        SharedMemory* aSegment, id_t aId);
#endif

  ~Shmem()
  {
    // Shmem only holds a "weak ref" to the actual segment, which is
    // owned by IPDL. So there's nothing interesting to be done here
    forget(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead());
  }

  Shmem& operator=(const Shmem& aRhs)
  {
    mSegment = aRhs.mSegment;
    mData = aRhs.mData;
    mSize = aRhs.mSize;
    mId = aRhs.mId;
    return *this;
  }

  // Return a pointer to the user-visible data segment.
  template<typename T>
  T*
  get() const
  {
    AssertInvariants();
    AssertAligned<T>();

    return reinterpret_cast<T*>(mData);
  }

  // Return the size of the segment as requested when this shmem
  // segment was allocated, in units of T.  The underlying mapping may
  // actually be larger because of page alignment and private data,
  // but this isn't exposed to clients.
  template<typename T>
  size_t
  Size() const
  {
    AssertInvariants();
    AssertAligned<T>();

    return mSize / sizeof(T);
  }

  // These shouldn't be used directly, use the IPDL interface instead.
  id_t Id(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead) {
    return mId;
  }

  void RevokeRights(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead)
  {
    Protect(mSegment);
  }

  void forget(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead)
  {
    mSegment = 0;
    mData = 0;
    mSize = 0;
    mId = 0;
  }

  static SharedMemory*
  Alloc(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
        size_t aNBytes,
        bool aProtect=false);

  // Return a SharedMemory instance in this process using the
  // SharedMemoryHandle (fd/HANDLE) shared to us by the process that
  // created the underlying OS shmem resource
  static SharedMemory*
  OpenExisting(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
               SharedMemoryHandle aHandle,
               size_t aNBytes,
               bool aProtect=false);

  static void
  Dealloc(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
          SharedMemory* aSegment);

private:
  template<typename T>
  void AssertAligned() const
  {
    if (0 != (mSize % sizeof(T)))
      NS_RUNTIMEABORT("shmem is not T-aligned");
  }

#if !defined(DEBUG)
  void AssertInvariants() const
  { }
  static void Unprotect(SharedMemory* aSegment)
  { }
  static void Protect(SharedMemory* aSegment)
  { }

  static size_t*
  PtrToSize(SharedMemory* aSegment)
  {
    char* endOfSegment =
      reinterpret_cast<char*>(aSegment->memory()) + aSegment->Size();
    return reinterpret_cast<size_t*>(endOfSegment - sizeof(size_t));
  }

#else
  void AssertInvariants() const;

  static void Unprotect(SharedMemory* aSegment);
  static void Protect(SharedMemory* aSegment);
#endif

  static SharedMemory*
  CreateSegment(size_t aNBytes,
                SharedMemoryHandle aHandle=SharedMemory::NULLHandle());

  static void
  DestroySegment(SharedMemory* aSegment);

  static size_t
  PageAlignedSize(size_t aSize);

  SharedMemory* mSegment;
  void* mData;
  size_t mSize;
  id_t mId;

  // disable these
  static void* operator new(size_t) CPP_THROW_NEW;
  static void operator delete(void*);  
};


} // namespace ipc
} // namespace mozilla


namespace IPC {

template<>
struct ParamTraits<mozilla::ipc::Shmem>
{
  typedef mozilla::ipc::Shmem paramType;

  static void Write(Message* aMsg, const paramType& aParam)
  {
    WriteParam(aMsg, aParam.mId);
  }

  // NB: Read()/Write() look creepy, but IPDL internally uses mId to
  // properly initialize a "real" Shmem

  static bool Read(const Message* aMsg, void** aIter, paramType* aResult)
  {
    paramType::id_t id;
    if (!ReadParam(aMsg, aIter, &id))
      return false;
    aResult->mId = id;
    return true;
  }

  static void Log(const paramType& aParam, std::wstring* aLog)
  {
    aLog->append(L"(shmem segment)");
  }
};


} // namespace IPC


#endif // ifndef mozilla_ipc_Shmem_h